A unit of Assured Guaranty Ltd. sued affiliates of Deutsche Bank AG over $312 million of mortgage- backed securities that the bond insurer guaranteed and says were “plagued by rampant fraud and misrepresentations.”

Assured Guaranty Corp. is asking a judge to force the bank to repurchase the loans, on which the insurer has already paid almost $60 million in loss claims and sees the potential for tens of millions of dollars more, according to a complaint filed today in New York state Supreme Court against DB Structured Products Inc. and ACE Securities Corp. The bond insurer, backed by billionaire Wilbur Ross, is also seeking reimbursement for the claims paid and for future losses.

“The entire pools of loans that Deutsche Bank securitized (and to a large degree originated) in the transactions are plagued by rampant fraud and misrepresentations and an abdication of sound origination and underwriting practices,” Assured said in the complaint.

Repurchases of home loans from buyers and insurers of mortgage securities originated before U.S. housing prices began to tumble in 2007 have already cost the four biggest U.S. lenders $9.8 billion, according to Credit Suisse Group AG.

Assured said more than 83 percent of 1,306 defaulted loans examined in one of the transactions, ACE’s Home Equity Loan Trust, Series 2007-SL2, breached Deutsche Bank’s representations and warranties. In the second deal, Home Equity Loan Trust, Series 2007-SL3, 86 percent of the 1,774 loans breached the agreements, Assured said.